A paper punch is a common device found in offices and schools. It is used to cut holes in paper under finger or hand pressure. Typically, a paper punch element includes a pin, and a frame to support the pin over a paper slot. The pin moves axially, or vertically, into the papers. It is desirable to minimize the force required to cut a hole into a stack of papers since these tools are usually operated under hand or finger pressure. To be sure, even a motorized paper punching device benefits from reduced force since a smaller motor may be used.
One method to reduce this force is to cut progressively around the perimeter of a hole rather than to cut the entire perimeter of the hole all at once. A well-known method for making a progressive cut is with a “V” cut notch in the end face of the pin. This creates more than one cutting point. The notched end cuts from two opposed sides of the hole toward the center of the hole. The notched end provides two equal pointed ends of the pin that press the paper stack simultaneously. Other designs use asymmetrical points or three or more cutting points.
Another concern is jamming of the pin in the paper. Typically, as the pin advances into the hole, the inside diameter edge of the paper is stretched and dragged down into the hole along with the pin. Then as the pin is withdrawn out of the hole, the edges tend to flip upward and press hard around the pin in a cam action. The hole effectively acts as a one-way cleat, with the hole inner diameter serving as a diaphragm to hold the pin in the hole. The hole diameter cut in the paper is in fact smaller than the diameter of the pin.
The prior art paper hole punches typically contemplate a compression type die spring strong enough to overcome the highest anticipated pull out or retraction force. The pin can typically be retracted only by the spring. Therefore, the spring must provide that function under all circumstances. U.S. Pat. No. 4,757,733 (Barlow) shows a typical arrangement in FIG. 6. Ridge 40 transmits pressure to cap 47 atop each pin (cutting tool 15). Helical spring 45 surrounds the pin. When the pin does not retract in this type of design, the paper becomes jammed in the punching device since there is no further way to force the pin out. This situation is familiar to most users of paper punches. Also, the force needed to compress the die spring directly adds to the hand or operating force required to cut the hole. When a small stack of papers is being cut, the spring force is often greater than the actual cutting force.
There are many hole punch tool and pin designs. For example, U.S. Pat. No. 5,730,038 (Evans et al.) shows a punch pin cutting end with specified groove depth in relation to a paper stack height, and a force sequence profile. U.S. Pat. No. 5,243,887 (Bonge, Jr.) shows a rectangular punch 18 fitted in the rectangular guide hole of a frame. The punch is pivotably attached to a lever and secured axially by pin 24. U.S. Pat. No. 4,763,552 (Wagner) discloses a punch pin with a symmetric angled cutting end. U.S. Pat. No. 4,713,995 (Davi) shows a conventional punch element design, including a helical return spring around the pin, and a lever that can only press, not pull, the pin. U.S. Pat. No. 4,449,436 (Semerjian, et al.) shows a cylindrical punch pin that includes a slotted top. A lever rib normally engages the top of the punch pin. An inoperative position for the sheet punch is achieved by rotating the punch pin so that the slot aligns with the lever rib. The rib then moves into the slot rather than pressing the top of the pin. No apparent mechanism is disclosed to keep the punch pin in its operative rotational position. The Semerjian '436 patent furthers shows an asymmetrical pin with one cutting point longer than another.
U.S. Pat. No. 4,257,300 (Muzik) discloses a cylindrical punch pin where the pin is secured axially at an annular groove. A key fitted in a radial slot of the pin positions the pin rotationally. U.S. Pat. No. 3,721,144 (Yamamori) shows a tubular punch die element with thin walls and a sharpened lower end. U.S. Pat. No. 3,320,843 (Schott, Jr.) shows a tubular punch element that is ground sharp at its cutting end. U.S. Pat. No. 4,594,927 (Mori) shows a punch pin held axially in two ways. In one embodiment, a rod 10 passes through a drilled hole in the upper body of the punch pin. Alternatively, an annular groove fits in a slot of a pressing plate. With the annular groove, the punch pin is not rotationally fixed in position. The Mori '927 patent shows an inclined base where the pins cut holes in a progressing sequence. The angle is very slight, just adequate to create the sequential cuts while maintaining a reasonable height to the punch device. U.S. Pat. No. 4,656,907 (Hymmem) shows a paper punch that may be disassembled for, among other reasons, to fix jammed pins. U.S. Pat. No. 4,240,572 (Mitsuhashi, et al.) shows a multi-pointed punch pin including a discussion of a punching sequence. U.S. Pat. No. 5,463,922 (Mori) shows a roller system for pressing punch pins in a sequence.
Japanese Patent Publication No. 64-087192 (Izumi, et al.) shows a punch pin with elongated cutting points, and a graph showing two force peaks during the punching operation. Japanese Patent Publication No. 61-172629 (Yukio) shows different cutting end profiles for a punch pin, including an asymmetrical end. U.S. Pat. No. 4,829,867 (Neilsen) shows a fixed diameter sleeve type punch pin with a helical cutting end. U.S. Pat. Nos. 6,688,199 (Godston, et al.) and 4,077,288 (Holland) disclose punches with a vertically oriented or upright paper slot. In the Godson '199 patent, the surrounding structure 532 holds the papers away from the user. As illustrated in FIGS. 4 and 9, slot 62 including floor 64 and ceiling 68 are perpendicular to the punch pin axis 50.